fix(#1455): resolve project-code-prefixed roadmap headings

* fix: remove hardcoded phase project-code prefix cap

Centralize project-code prefix stripping/matching and replace fixed {1,6} caps so long codes (for example MANIFOLD-117) resolve across phase, roadmap parser, roadmap upgrade, and validate flows.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: address review feedback on prefix parsing

- allow project_code prefixes with digits and underscores while preserving milestone parsing
- use shared optional project-code prefix source in phase dir parsing
- extend regression coverage for APP1/APP_1 prefixed phases

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: resolve review nit in phase-id test comment

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: resolve project-code-prefixed roadmap headings

Make getRoadmapPhaseInternal recover from drifted project-code-prefixed ROADMAP headings while preserving canonical bare-heading preference. Add init.phase-op and parser regressions for #1455 and guard gsd-roadmapper against emitting project_code in headings.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: add changeset for project-code phase fix

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: update roadmapper agent size baseline

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix(#1455): tighten project-code prefix regex to [A-Z] start; add boundary test; document source order

Resolves blockers from review:
- Regex changed from [A-Z_][A-Z0-9_]* to [A-Z][A-Z0-9_]* so leading
  underscores (_FOO-7, _-7) are never misread as project-code prefixes;
  adds boundary test asserting both do NOT strip.
- Adds comment to roadmapPhaseLookupSources explaining why 3 sources are
  needed (order-dependent canonical-heading preference).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Solvely-Colin <211764741+Solvely-Colin@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/validate.cts

@@ -31,14 +31,24 @@
  *   - PR #156 (issue #6) — validate.ts generator that #26 extends
  */
 
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import phaseIdMod = require('./phase-id.cjs');
+const { OPTIONAL_PROJECT_CODE_PREFIX_SOURCE } = phaseIdMod;
+
 // ── Issue #26: regex constants (W005, W006-archived) ────────────────────────
 // Matches legacy numeric dirs (01-setup), milestone-prefixed dirs (02-01-setup),
 // deep dirs (02-04-01-deep), and project-code-prefixed variants (GSD-02-01-setup).
-export const phaseDirNameRe = /^(?:[A-Z]{1,6}-)?\d{2,}(?:-\d+)*(?:\.\d+)*-[\w-]+$/i;
+export const phaseDirNameRe = new RegExp(
+  `^${OPTIONAL_PROJECT_CODE_PREFIX_SOURCE}\\d{2,}(?:-\\d+)*(?:\\.\\d+)*-[\\w-]+$`,
+  'i',
+);
 // Extracts the full phase token from a directory name, including milestone-prefixed
 // multi-segment tokens like "02-01" from "02-01-setup" or "GSD-02-01-setup".
 // Greedily captures all leading all-digit segments before the first letter-start segment.
-export const PHASE_TOKEN_FROM_DIR_RE = /^(?:[A-Z]{1,6}-)?(\d+(?:-\d+)*[A-Z]?(?:\.\d+)*)(?:-[a-z]|$)/i;
+export const PHASE_TOKEN_FROM_DIR_RE = new RegExp(
+  `^${OPTIONAL_PROJECT_CODE_PREFIX_SOURCE}(\\d+(?:-\\d+)*[A-Z]?(?:\\.\\d+)*)(?:-[a-z]|$)`,
+  'i',
+);
 export const MILESTONE_ARCHIVE_DIR_RE = /^v\d+.*-phases$/i;
 
 // ── Issue #26: I001 canonicalization ────────────────────────────────────────